UTC Scroll

How to use this application

Click and drag the time-displays with the mouse or use the scrollwheel.

You can also enter the values in the textfields.

The button Now sets the time to the current system-time and stays in sync with the system time up until the time is changed manually.

The button Local sets the timezone to the current system-timezone and stays active up until the timezone is changed manually.

When you click on the arrow at the bottom right corner, you can control time!

Year Zero

The year zero exists when using astronomical year numbering. In astronomical year numbering, year is just a number which can be zero or even negative. The year zero denotes the year just before christ birth which is the defining base in christian timekeeping where years are denoted as ordinal numbers before and after Christ birth.

UTC is defined to use astronomical year numbering.

To convert between negative year numbers and christinan year numbering, use the following rule: Year 0 corresponds to 1 BC, year -1 corresponds to 2 BC, year -2 corresponds to 3 BC... The abbreviation BC denotes before Christ. There exist many different abbreviations, some with and some without reference to Christ.

Leap Years

One year consists of approximately 365¼ days. This is the time it takes for the earth to travel around the sun once. Humans are strongly connected to the periodic repetition of the course of a day, and therefore, a ¼ day is not desirable. Though when a year only can contain a whole number of days, where to put the additional ¼ day?

In order to make every year seemingly equal, the ¼ day must be somehow distributed. In julian calender, an additional day at the end of every forth year was added. As in julian calender, the first month of the year was March, the additional day was therefore added at the end of February. A year containing such an additional day is called a leap year.

With time, people detected that a year is not comprised of exactly 365¼ days but rather more approximately 365.2425. Therefore after some centuries, there were approximately 10 days too much due to the additional days of the leap years. In the year 1582, the gregorian reform corrected this error, going from 4th of october directly to 15th of october. Since then, year numbers which can be divided by 100 are explicitely no leap year, unless the year can be divided by 400.

Leap Seconds

In traditional timekeeping, a second is defined to be the 86400th part of a day (24 hours with 60 minutes with 60 seconds). The course of one day is defined by the earths rotation. This is the normal second we use everyday and is reflected in the Coordinated Universal Time (UTC). In science though, a second is defined by atomic clocks which measure the periodic frequency of the state of atoms. This second is called an SI-second. The definition of the SI-second was proposed to be approximately equal to the traditional second. The final definition of the base unit was fixed on January 1st 1958 00:00 and defined the International Atomic Time (TAI).

Unfortunately, due to astronimical influences, the earths rotation is fluctuating and overall being slowed down. As the definition of an SI-second is not bound to the earths rotation, the two definitions of a second slowly deviate. This process is very slow relative to human timekeeping.

It was decided that one international organization has to observe the earths rotation and define, when to correct the coordinated world time (UTC) such that both UTC and TAI can share the same definition of the second: The SI-second. This correction is done by introducing leap seconds at precisely defined dates. Currently, leap seconds are introduced at the end of June or at the end of December. When precisely these leap seconds occur is published some months in advance in an open letter (Bulletin C).

For example, June 30th 2015 contains a leap second. On this day, the clock shows 23:59:59, followed by 23:59:60, followed by 00:00:00.